It is well known to construct generally flat roofs on some buildings, especially commercial buildings having a roof area of several hundreds or thousands of square feet. (The phrase "flat roof" is being used herein in the manner in which many people customarily refer to roofs that are at least generally planar and essentially horizontal--not just planar.) It is also known to try to make flat roofs weather-tight by providing what is called a built-up series of horizontal layers of felt and the like, sealed with asphalt (or bitumen), and covered with gravel, etc. However, such built-up roofs are seldom effective in remaining water-tight for more than a few years; and depending on seasonal variations in temperature, sometimes even a single year can constitute the effective life of a roof--before it needs repair. One measure of the confidence that professional roofers have in their work is the length of time that they will put into a written guarantee of a flat roof when they install it. A few roofers may guarantee their work for several years, but others may offer a guaranty of only one year; some may even opt for their own financial security (or that of their business) by putting no guaranty on their work other than the fact that the roof won't leak on the day that they finish their job.
There are probably three primary masons why roofers are reluctant to take on the financial gamble of guaranteeing the long-term integrity of a flat roof. First, roofers generally have no control over the quality of a building's foundation, and they can never know with certainty whether the foundation will support a building with the rigidity that will ensure that a roof will not be subjected to the destructive shifting that will create major stresses and eventual fissures. Certainly, if a building is going to shift on an unstable foundation, a roof that is not flexible will not be able to move in such a way that it has some chance at remaining intact. Second, over time, a roof will inevitably be subjected to major stresses because of ordinary temperature changes, even if a building's foundation and superstructure remain relatively stable. Because the roof is located at the top of a building, it often is not shaded by anything; and a very large roof may change size by several inches in a single day--as it cools to, say, 65.degree. F. at night and warms to 95.degree. F. the next afternoon. Even more rapid changes can occur if a thunderstorm pours cooling rain onto a hot roof on a building in the middle of August, when the temperature in the shade (in a place like the Southwestern United States) is over 100.degree. F. Any quick changes in the temperature of a rigid roof can introduce the kind of expansion and contraction that will almost surely create cracks, which will eventually allow rain water to flow into a building. Third, roofs of the prior art have been particularly susceptible to damage as a result of exposure to ultraviolet (abbreviated "UV") radiation, and it is hard for a roofer to anticipate how much UV radiation can be expected, or how it will affect a given roofing material.
It should not be surprising, therefore, that there has been a need for an improved technique for covering the generally flat (or low-pitch) roof of a building with a waterproof cover that is not subject to failure as a result of normal environmental conditions. And it is an object of this invention to provide such a technique. But it probably should be acknowledged at this point that others have not been totally inactive in this field. Indeed, U.S. Pat. No. 4,965,977 to White entitled "Insulated Panelized Roofing System" provides a description of at least four types of "commercial" constructions for flat or low-slope roofs: 1) torched-on single-ply; 2) EPDM single-ply; 3) built-up, also known as BUR; and 4) panelized. The last-named of the four types of roofs was supposedly created in order to overcome the many deficiencies of the first three. But even White acknowledges that panelized roofs have not solved all of the problems of the industry. In fact, it is believed that the 1990 characterization of the prior art by White is still valid today, and is worth repeating here: " The panelized roofing systems have suffered from numerous shortcomings including relatively high cost, difficulty in curing the panel boards, the requirement of open-torch flame application, easily damaged insulation boards, and physical irritation caused by fiberglass or rock wool insulation materials".
Because of the long-standing problems of flat and low-slope roofs of the prior art, it is believed to be clearly justified to move in a new direction for waterproof coverings for roofs. But the new construction that is to be revealed hereinafter can best be described with at least some terms (e.g., panels) that will, at first blush, sound familiar. In view of the valid criticisms by White and others, it is believed to be appropriate to point out that this is not just another rehash of a failed concept.